1. Field of the Invention
This invention relates to telomers of chlorotrifluoroethylene. More particularly, this invention relates to novel iodine-terminated telechelic telomers of chlorotrifluoroethylene that are prepared from elemental iodine and chlorotrifluoroethylene.
2. Background Information
Bifunctional or telechelic telomers derived from fluorinated olefins are known and are becoming increasingly important based on their desirable properties, particularly insolubility in organic liquids and thermal stability. For example, telomers of tetrafluoroethylene prepared by reacting ICF.sub.2 CF.sub.2 I with CF.sub.2 =CF.sub.2 are reported by V. Tortelli and C. Tonelli in the Journal of Fluorine Chemistry [43 (1990), p. 199].
Addition reaction products of chlorotrifluoroethylene (CTFE) with fluorine, chlorine, bromine and the interhalogens BrF, IF, ICl, and IBr are reported and have been well characterized in the chemical literature. These products have been prepared by heating or the use of free radical initiators such as peroxides. Photochemical initiation of the reactions is not reported.
The reaction of chlorotrifluoroethylene with elemental iodine is reported by J. T. Barr et al. (J. Amer. Chem. Soc., 1951, 73, 1352. A mixture containing equal weights of the reactants was sealed in a glass tube and allowed to stand for several days under ambient conditions. The resultant liquid product, thought to be 1-chloro-1,2,2-trifluoro-1,2-diiodoethane, was distilled in 30-35% yield and boiled from 54.degree.-55.degree. C. under a pressure of 20 mm Hg. The product decomposed upon standing to yield iodine and no other isolatable product, and was not sufficiently stable to be analyzed. By comparison, the reaction product of chlorotrifluoroethylene with iodine monochloride was stable and was characterized as CF.sub.2 ClCFClI.
M. Hauptschein et al. [JACS 79, 2549 (1957)] describes the reaction of chlorotrifluoroethylene with the stable telogen reported by Barr, namely CF.sub.2 ClCFClI, at a temperature of 200.degree. C. using a spiral tube reactor that minimized contact time between the reactants. The product contained 22 weight percent each of the telomers CF.sub.2 ClCFCl(C.sub.2 F.sub.3 Cl).sub.n I where the value of n was 1, 2, or 3 and 33 weight percent of telomers wherein n was 4 or greater.
R. Haszeldine [J.C.S. 4291 (1955)] describes the telomerization of chlorotrifluoroethylene in the presence of the telogen ClCF.sub.2 CFClI and ultraviolet light or heat to yield telomers. Telomers containing up to 20 repeating units per molecule are characterized as liquids. The author proposes using peroxides as the free radical source for large scale reactions.
The article by Haszeldine makes no mention of using the bifunctional telogen ICF.sub.2 CFClI, reported as unstable in the aforementioned article by Barr et al., to initiate the telomerization of chlorotrifluoroethylene (CTFE). Based on the instability of this telogen reported by Barr et al. it is unlikely that one would consider substituting it for the telogen ClCF.sub.2 CFClI reported by Haszeldine.
The present inventor therefore considered it surprising to discover that when iodine is combined with more than an equimolar amount of CTFE the iodine will react substantially completely in the presence of ultraviolet or visible radiation to initially produce the telogen reported by Barr et al. Upon further exposure to radiation the telogen is gradually converted to stable telomers represented by the general formula I(CF.sub.2 CFCl).sub.n I, where the average value of n is greater than 1. The value of n for a particular product is determined by the reaction conditions, specifically the type of radiation, exposure time, and the reaction temperature.
The bifunctional telomers of CTFE can be reacted with fluorine, olefins or fluoroolefins to obtain products in the form of liquids, solids and greases.
The present inventor also discovered that the bifunctional telogen ICF.sub.2 CFClI can be isolated if the reaction of CTFE and iodine is conducted in the presence of visible light or gamma radiation. Contrary to the teaching of Barr et al. the telogen is stable when stored in the dark at temperatures below about 30.degree. C.